The invention relates to a write/read device designed for the contactless communication with at least one transponder and comprising data supply means for supplying at least one data block and including first coding means, by which first coding means a data block supplied by the data supply means and applied to said first coding means can be coded in accordance with a first coding method and by which, as a result of the coding in accordance with this first coding method, at the most a given number N of coding signals representing a data block can be generated and supplied, and including carrier signal generating means for generating a carrier signal and including modulation means, to which modulation means the carrier signal and the coding signals can be applied and by which modulation means the carrier signal can be modulated in accordance with the coding signals so as to generate and supply a modulated carrier signal corresponding to the number of coding signals and having the same number of modulation steps, and including transmission means, to which transmission means the modulated carrier signal can be applied in order to be transmitted to at least one transponder.
Such write/read device is commercially available in a variety of versions and is consequently known. The known write/read device includes coding means adapted to perform a bit-oriented coding method, wherein for coding a data block a given number N of bits can be coded, i.e. each bit can exhibit either the logic zero state or the logic one state, so that as a result of coding in accordance with this bit-oriented coding method at the most a given number N of coding signals, i.e. coding pulses, which represent a data block can be generated. Such a bit-oriented coding method has the advantage that a component high transmission rate is attainable. However, such a coding method entails the problem that corresponding to each coding signal a modulation step occurs in the carrier signal, which is amplitude-modulated in the known write/read device, as a result of which during the transmission from the write/read device to a transponder not only the amplitude-modulated carrier signal has a comparatively high amplitude but that, in addition, the amplitudes in the so-called sidebands may exhibit comparatively large values if many modulation steps occur, which in many countries gives rise to problems as regards statutory regulations relating to spurious emission and the limitation of spurious emission.
It is an object of the invention to preclude the afore-mentioned problems in a write/read device and to provide an improved write/read device during whose use no problems arise as regards statutory regulations relating to spurious emission and the limitation of spurious emission. According to the invention this object is achieved in a write/read device of the type defined in the opening paragraph in that there have been provided second coding means, by which second coding means a data block supplied by the data supply means and applied to said second coding means can be coded in accordance with a second coding method and by which second coding means, as a result of coding in accordance with said second coding method, at the most a given number M of coding signals representing a data block can be generated and supplied, the number M being smaller than the number N, and there have been provided selection means with the aid of which it is possible to select that the coding signals representing a data block and supplied by the first coding means or that the coding signals representing a data block and supplied by the second coding means can be applied to the amplitude modulation means. By means of the measures in accordance with the invention it is achieved in a very simple manner and with only minimal additional cost that in a write/read device in accordance with the invention it is possible to choose from two coding possibilities or coding methods, so that it is possible either to select a coding method in which high amplitudes can occur in the range of the sidebands but which has the advantage that it guarantees high transmission rates, i.e. a transmission which is as rapid as possible, or to select another coding method which only allows a lower transmission rate, i.e. a slower transmission, but which has the advantage that it guarantees particularly small amplitude values in the range of the sidebands, thereby ensuring that problems as regards statutory regulations relating to maximum permissible spurious emissions and the limitation of spurious emission are avoided.
In a write/read device in accordance with the invention the measures defined in claim 3 have proved to be advantageous because it is thus the desired result is obtained with a minimal number of modulation steps in the modulated carrier signal per coded data block, which guarantees particularly small amplitude values in the range of the sidebands.
Various possibilities are available for the implementation of the selection means in a write/read device in accordance with the invention. However, it has proved to be particularly advantageous if the measures defined in claim 4 are taken because this has appeared to be particularly favorable for implementation by means of a microcomputer.
The measures defined in claims 5 and 6 have proved to be very advantageous because they guarantee that in a transponder which communicates with a write/read device in accordance with the invention the coding method selected for the data transmission in the write/read device can be detected very simply and thus a correct decoding is guaranteed in the transponder.
The afore-mentioned as well as further aspects of the invention will become apparent from the example of an embodiment described hereinafter and will be elucidated with reference to this example.